problem with ALTER GROUP

Please help! Unfortunetely I gave numbers for user names (column "usename" in
pg_shadow). Now in 7.0 we have ALTER GROUP, but the statement

test=# ALTER GROUP anygroup ADD USER 1234;

where 1234 can be any number, will result this error message:

ERROR:  parser: parse error at or near "1234"

I couldn't find any workarounds yet. No conversions solved my problem.
Any ideas?

Regards,
Zoltan